The specifics are as follows:

— Coalition forces heard an explosion at 4:44 a.m. this morning about 12 miles west of Mahmudiyah;

— After an unmanned aerial vehicle observed two burning vehicles, a quick reaction force was dispatched, arriving on scene at 5:40 a.m.;

— The quick reaction force reported finding five members of the team killed in action and three others whose duty status and whereabouts are unknown;

— Helicopter, unmanned aerial vehicle, and fixed wing assets are being used to search in the vicinity;

— Checkpoints have been established throughout the area in a concerted effort to focus the search and prevent potential movement of missing soldiers out of the area;

— Coalition forces have engaged with local leaders to enlist their support in providing any information they can, and these engagements continue.

"At the time of the attack, a nearby unit heard explosions and attempted to establish communications, but without success," he said in a statement.

"Coalition forces arrived within an hour, secured the site, and immediately initiated a search. The names of the soldiers are being withheld pending final identification and notification of next of kin," he said.

"Make no mistake: We will never stop looking for our soldiers until their status is definitively determined, and we continue to pray for their safe return," he added, as helicopters and jets were scrambled to join the hunt.

Mahmudiyah lies 30 kilometres (20 miles) south of Baghdad in an area of farmland and palm groves known as an insurgent stronghold. Since the US invasion of March 2003 the region has been nicknamed the "Triangle of Death".

Earlier, US marines on patrol on a road west of Baghdad near the restive city of Fallujah told an AFP reporter travelling with them that they had been told the missing soldiers were thought to have been captured.

"We got word about 0900 (0400 GMT) that three soldiers were missing. Last we heard was that they were headed in this direction, presumed captured," said Gunnery Sergeant James Curtis of the US Marines 2nd Battalion 6th Regiment.

Curtis's patrol threw up a checkpoint on a stretch of road on the eastern edge of Fallujah in a bid to intercept the abductors if they attempted to bring their captives there from the area west of Baghdad.

Some of the trucks and cars arriving at the roadblock were marked as having been searched, showing that other military checkpoints had been set up on the road, which leads from Fallujah towards both Mahmudiyah and the capital.

"Checkpoints have been established throughout the area in a concerted effort to focus the search and prevent potential movement of missing soldiers out of the area," Caldwell's statement said.

"Coalition forces have engaged with local leaders to enlist their support in providing any information they can, and these engagements continue."

The military refused to specify whether the Iraqi interpreter was among those killed or among the missing or give more details about where the bodies were found.

An Iraqi army officer, who was familiar with the search but spoke on condition of anonymity because he was not authorized to disclose the information, said he saw five badly burned bodies inside a Humvee at the attack site, suggesting the remains may not have been recognizable.

He also said joint U.S.-Iraqi forces had sealed off the area and were conducting house-to-house searches in the area, rounding up dozens of suspects. The military declined to comment on detentions but said troops were looking for suspects.

The Iraqi officer said U.S. troops singled out seven suspects out of as many as 50, including a wounded man who was hiding in a house and confessed to participating. He said most of the houses searched near the attack contained only women and children because the men had fled after hearing news of the attack, fearing arrest.